Merriam-Webster's Word of the Day

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Build your vocabulary with Merriam-Webster's Word of the Day! Each day a Merriam-Webster editor offers insight into a fascinating new word -- explaining its meaning, current use, and little-known details about its origin.

sidereal

Merriam-Webster's Word of the Day for March 30, 2016 is: sidereal \sye-DEER-ee-ul\ adjective 1 : of or relating to stars or constellations 2 : measured by the apparent motion of the stars Examples: David's parents were so pleased by his newfound interest in sidereal phenomena that they bought him an expensive telescope for his birthday. "Today, these various astronomical functions can mainly be found in very complicated watches…. These exceptional timekeepers are masterpieces of knowledge, technique and know-how, presenting a range of complex functions: display of sidereal time, equation of time, hours of sunrise and sunset, star charts, angular movement of the moon, phases of the moon...." — Grégory Gardinetti, CNN.com, 6 Jan. 2016 Did you know? In Latin, the word for a star or constellation is sidus. Latin speakers used that word to form desiderare ("from a heavenly body") and considerare ("to think about a heavenly body"), which were adopted into English as desire and consider. Sidereal, another sidus creation, was first documented in English in 1642. Thirty-four years later, an astronomer coined the phrase "sidereal year" for the time in which the earth completes one revolution in its orbit around the sun, measured with respect to the fixed stars. Not surprisingly, other sidereal measurements of time followed, including the sidereal month, the sidereal day, the sidereal hour, and even the sidereal minute.